1. Field of the Invention
The present invention relates to a spiral cable device, which is suitable for use in, for example, a variable gear ratio steering device of vehicles.
2. Discussion of the Related Art
Japanese unexamined, published patent application No. 10-164745 (1998-164745) discloses a prior art spiral cable device. As shown in FIG. 6(c), the cable device is provided with a cylindrical casing 90, an inner cylinder 91 rotatable relative to the cylindrical casing 90 within the same, and a flexible flat cable 92 connected to the inner cylinder 91 at one end thereof and to the cylindrical casing 90 at the other end thereof to be wound around the inner cylinder 91. As shown in FIGS. 6(A) and 6(B), the flexible flat cable 92 is composed of plural leads 92a which are coated with flexible resin 92b to be isolated electrically.
The spiral cable device is employed to electrically connect the members which are relatively rotatable with each other in a variable gear ration steering device, an air bag device or the like of vehicles. Where the spiral cable device is used in, for example, a variable gear ratio steering device of a vehicle, the cylindrical housing 90 is fixed to a vehicle body, while the inner cylinder 91 is fixed to a housing of the variable gear ratio steering device. Further, one end of the flexible flat cable 92 is connected to the inner cylinder 91 by means of a terminal 93, and leads extending from the inner cylinder 91 are connected to a stator of a motor or the like. On the other hand, the other end of the flexible flat cable 92 is connected to the cylindrical casing 90 by means of a terminal 94, and leads extending from the cylinder casing 90 are connected to a battery and an ECU (Electronic Control Unit) of the vehicle. In the spiral cable device, when the cylindrical casing 90 and the inner cylinder 91 are rotated relative to each other, the battery and the ECU are maintained connected electrically with the stator of the motor as long as the angle of the relative rotation therebetween is within the winding range of the flexible flat cable 92.
However, in the prior art spiral flat cable device, the flexible flat cable 92 arranges the plural leads 92a within a single layer and is wound to form only a single layer of the leads 92a in the radial direction of the winding. Thus, where the flexible flat cable 92 is of the type that the plural leads 92a are coated to be isolated electrically, the flexible flat cable is caused to be large in width so that the cylindrical casing 90 containing the flat cable 92 and the inner cylinder 91 are enlarged in the axial direction thereof. This disadvantageously causes the axial length of the spiral cable device to be enlarged. Therefore, when the spiral cable device were employed in the aforementioned variable gear ratio steering device, air bag device or the like of the vehicle, the axial length of the same would be enlarged thereby affecting the capability of being mounted on vehicles or the like.